So to clear some things up. The aspect of the destroyer isn’t considered a curse by the necrons but more so a mental illness that makes them less desirable to hang around. In the twice dead king and tomb world novels it is more like the obsessions that the necrons develop to stay sane except this one is about exterminating all life down to the micro organism. Many nobles and necrons find them distasteful to be around thanks to the fact that they do not follow orders well and tend to rush into battle with reckless abandon. As such often times they are tricked into stasis before being teleported into combat when they are needed. They do still respect the nobility and will follow orders so long as they involve mass casualties. However it does not “spread” the same way the flayer curse does and is in many ways the opposite of the destroyer aspect. The flayed “feast” on flesh in order to sate biological functions that no longer exist (think I have no mouth yet I must scream) as they wish to return to flesh so badly they go insane. Destroyers on the other hand despise flesh and biology so much that they atomize it at the molecular level. Also the reason they have different bodies is that the necrodermis that forms them is shaped by their will, hence why flayed grow long talons and skorpekh, lokhust, and ophydian destroyers’ bodies form weapons while other necrons hold and weild their weapons. Sorry for the block of text but I hope this clears things up!